1. Field of the Invention
The present invention relates to a pulse counter for counting a pulse train outputted in response to the rotation of an electric motor, and more particularly, to a pulse counter used for simultaneously controlling a plurality of electric motors in a highly accurate manner.
2. Description of the Prior Art
In an electric motor driving device which simultaneously drives two electric motors, it is usual to control revolutions of each electric motor by inputting the pulse trains outputted from the electric motors and counting the difference between the pulse numbers outputted from the electric motors with a pulse counter.
To create the pulse train from the electric motor, a pulse generator is mounted on each of the electric motors. The pulse generated by the pulse generator has a very high frequency. This leads to a problem in that there is a limitation to processing the high frequency outputted pulse.
It is usual that the number of pulses per revolution generated by the pulse generator is not fixed and changes in response to the machines which are driven by the electric motors and the applications to which those machines are subject.
When an incremental pulse generator is used, it is difficult to obtain synchronized operation of two electric motors and keep an absolute phase difference between the two electric motors at all times.
It is an object of the present invention to provide a pulse counter capable of counting high frequency pulses and easily dealing with such high frequency pulses even though the number of pulses per revolution generated from the pulse generator is different. Furthermore, the present invention detects an absolute phase difference between a plurality of the electric motors.